Phase change memory stack with treated sidewalls

ABSTRACT

Memory devices and methods for fabricating memory devices have been disclosed. One such memory device includes a first electrode material formed on a word line material. A selector device material is formed on the first electrode material. A second electrode material is formed on the selector device material. A phase change material is formed on the second electrode material. A third electrode material is formed on the phase change material. An adhesion species is plasma doped into sidewalls of the memory stack and a liner material is formed on the sidewalls of the memory stack. The adhesion species intermixes with an element of the memory stack and the sidewall liner to terminate unsatisfied atomic bonds of the element and the sidewall liner.

BACKGROUND

Memory devices are typically provided as internal, semiconductor, integrated circuits in apparatuses such as computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and non-volatile (e.g., phase change memory, flash) memory.

Non-volatile memories are important elements of integrated circuits due to their ability to maintain data absent a power supply. Phase change materials have been investigated for use in non-volatile memory cells. Phase change memory (PCM) elements include phase change materials, such as chalcogenide alloys, that are capable of stably transitioning between amorphous and crystalline phases. Each phase exhibits a particular resistance state and the resistance states distinguish the logic values of the memory element. Specifically, an amorphous state exhibits a relatively high resistance and a crystalline state exhibits a relatively low resistance. One of different logic levels (e.g., logic 1 or logic 0) can be assigned to each of these states.

Thus, there are general needs to improve PCM devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a typical phase change memory stack.

FIGS. 2-7 illustrate an embodiment of a process flow to fabricate a phase change memory stack having treated sidewalls.

FIG. 8 illustrates a detailed cross-sectional view of an embodiment of intermixing of an implanted adhesion species on memory stack sidewalls.

FIG. 9 illustrates a block diagram of a memory system in accordance with the embodiments of FIGS. 2-8.

DETAILED DESCRIPTION

As described subsequently, a method for fabricating a memory stack (e.g., memory device) with treated sidewalls can increase the adhesion of dielectric passivation material to the electrodes. This can reduce inter-diffusion between the electrodes and adjacent materials in the memory stack.

FIG. 1 illustrates a typical memory cell stack for a PCM. Carbon can be used as top 101, middle 102, and bottom 103 electrodes for the memory cell stack. Carbon is chemically inert and does not react easily with the phase change material 110 or the selector device material 111. This inert chemistry can also lead to poor adhesion of sidewalls to the carbon electrodes. As a result, it can be possible for the sidewall material 120, 121 to inter-diffuse 130, 131 between the selector device material 111 and the phase change material 110. This can occur at higher temperatures. The inter-diffusion can cause reliability issues, degrade leakage current, and affect threshold voltage stability.

FIGS. 2-7 illustrate various steps in fabricating a memory stack (e.g., PCM) in addition to treating the sidewalls of the memory stack with an adhesion species. These fabrication steps are for purposes of illustration only as the different elements of the stack can be formed by different processes.

FIG. 2 illustrates an embodiment of a blanket deposition of the initial memory stack material 200. The memory stack can include a word line material (e.g., tungsten (W)) 201. A first electrode material 202 (e.g., carbon) can be formed on the word line material 201. A selector device material 203 may be formed on the first electrode material 202.

The selector device material 203 (SD) may include Selenium (Se), Arsenic (As), Germanium (Ge), Tin (Sn), Tellurium (Te), Silicon (Si), Lead (Pb), Carbon (C), or Bismuth (Bi) as well as other materials. Other embodiments can include selector device material 203 comprising one or more of these elements as well as one or more of these elements combined with other elements.

A second electrode material 204 (e.g., carbon) can be formed on the selector device material 203. A phase change material 205 can be formed on the second electrode material 204.

The phase change material 205 (PM) can include chalcogenide elements such as Germanium (Ge), Antimony (Sb), Tellurium (Te), Indium (In) as well as other chalcogenide elements, combinations of these elements, or combinations of these elements with other elements. The phase change material 205 can additionally include Aluminum (Al), Gallium (Ga), Tin (Sn), Bismuth (Bi), Sulphur (S), Oxygen (O), Gold (Au), Palladium (Pd), Copper (Cu), Cobalt (Co), Silver (Ag), or Platinum (Pt) as well as other elements. Additional embodiments can combine these elements with the chalcogenide elements.

A third electrode material 206 (e.g., carbon) can be formed on the phase change material 205. Forming the third electrode material 206, as well as the other materials 201-205 of the memory stack, can be done with a blanket deposition method or some other deposition method.

After the initial memory stack material 200 has been formed, an etch process (e.g., dry etch) can be performed on the stack material 200 to create trenches 301-304 as illustrated in FIG. 3. FIG. 3 illustrates that the stack material 200 has been divided by the plurality of trenches 301-304 into a plurality of memory stacks 311-315, each stack comprising the architecture illustrated in FIG. 2. In some embodiments (not shown), a plurality of trenches is formed in the stack material to less than its full height.

In another embodiment, the stack material 200 can be dry etched patterned in both x and y directions. Thus, subsequent sidewall liners can be added on four sidewalls, as illustrated in FIG. 7.

FIG. 4 illustrates the treatment of the sidewalls or sidewall liners (as seen in FIG. 5) of particular ones of the stacks 311-313 as formed in FIG. 3. This treatment enhances the dielectric liner adhesion to the electrode surfaces. In an embodiment, a plasma immersion technique (e.g., plasma doping (PLAD)) can be used to implant an adhesion species 401-403 in either the stack sidewalls or the sidewall liners.

In an embodiment, the dielectric sidewalls or sidewall liners (as seen in FIG. 5) can be treated with an adhesion species 401-403 (e.g., boron) by exposing the sidewalls to the adhesion species mixed in a carrier gas. For example, boron can be mixed with a flourine carrier gas such that the sidewalls or the sidewall liners are exposed to the boron triflouride (BF₃) during the plasma doping, as illustrated in greater detail with reference to FIGS. 4 and 8. Boron has properties that are between metals and non-metals. Chemically it is more related to silicon than to aluminum, gallium, indium, or thallium. Fluorine is electro-negative and reactive of all elements and reacts with most organic and inorganic substances.

Relatively low energy plasma immersion implant can have advantages if used in this process. For example, conformal doping can be used in the process in order to achieve a tunable implant/deposition operation regime and a shallow profile. The ion bombardment nature of an implant process can enhance an adhesion-friendly species (e.g., boron) by intermixing with the electrode material. For example, the implanted adhesion species can improve adhesion by species intermixing and terminating unsatisfied atomic bonds (e.g., carbon bonds). Other adhesion species 401-403 that have substantially similar properties can also be used. To form the PCM cells, electrically insulated pillars are formed (e.g., by dry etching) in the bit line direction while the memory stacks are formed in the word line direction.

FIG. 5 illustrates an embodiment for forming the sidewall liners 500-508 on the sidewalls of the stacks 311-315. The process to form the sidewall liners 500-508 can include any dielectric material that can be deposited by any deposition process. For example, the sidewall deposition can include a Plasma Enhanced Atomic Layer Deposition (PEALD) process using a dielectric material such as AlSiO_(x). Any dielectric material can be used during the sidewall deposition.

FIG. 6 illustrates an embodiment for forming a dielectric fill material 601-604 between adjacent memory stacks. The dielectric fill material 601-604 can electrically isolate each of the memory stacks. The dielectric fill material 601-604 can be the same material as the sidewall liners 500-508 or a different dielectric material.

FIG. 7 illustrates an embodiment for forming additional decks of memory stacks. For example, FIG. 7 shows two memory stacks 701, 702 coupled together at a common bit line 703. The sidewalls or the sidewall liner treatment described previously with reference to FIG. 4 and below with reference to FIG. 8 may be repeated for the memory stacks at each of the decks. Other embodiments can have additional decks of memory stacks 701, 702.

FIG. 8 illustrates a detailed cross-sectional view of an embodiment of intermixing of an implanted adhesion species on memory stack sidewalls. The implanted adhesion species has been shown and described as being implanted into the sidewalls of the memory stacks but other embodiments may implant the adhesion species into the sidewall liners.

FIG. 8 shows an enlarged detail view 820 of the atomic level intermixing boundary 810 between the second electrode material 803, the adhesion species, and the memory stack liner 801. This diagram shows that the adhesion species (e.g., boron) intermixes with the material of the electrode (e.g., carbon) and the liner 801 to cause enhanced adhesion of the liner 801 to the electrode material 803. The intermixing can be accomplished by the adhesion species terminating unsatisfied atomic bonds of both the electrode material 803 and the liner 801.

The represented sequence of layers is for purposes of illustration only. Other embodiments can use other sequences. For example, the relative position of the PM and select material (SD) may be exchanged. Also, the relative positions of word line material and bit line material may be changed (e.g., having bit lines at the bottom of the first deck and word lines at the top of the first deck and possibly shared with a second deck stack.

FIG. 9 illustrates a block diagram of a memory system that include a memory device 901 that can use the memory stacks with treated sidewalls of FIGS. 2-8. A controller 900 may be used to control operations of the system. The memory device 901, coupled to the controller 900, may include a memory array comprising memory cell stacks as described above with reference to FIGS. 2-8.

The controller 900 may be coupled to the memory device 901 over control, data, and address buses. In another embodiment, the address and data buses may share a common input/output (I/O) bus. The controller 900 can be part of the same integrated circuit as the memory device 901 or as separate integrated circuits.

As used herein, an apparatus may refer to, for example, circuitry, an integrated circuit die, a memory device, a memory array, or a system including such a circuit, die, device or array.

CONCLUSION

One or more embodiments of the method for memory stack sidewall treatment can result in a memory device with memory stacks having enhanced adhesion to the sidewall liners. For example, an adhesion species (e.g., boron) can intermix with particular materials of the memory stack to create better adhesion and, thus, reduced sidewall material inter-diffusion. The sidewalls can be treated with the adhesion species using a BF₃ PLAD sidewall treatment.

Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiments shown. Many adaptations will be apparent to those of ordinary skill in the art. Accordingly, this application is intended to cover any adaptations or variations. 

What is claimed is:
 1. A method for fabricating a memory stack, the method comprising: forming the memory stack out of a plurality of elements; forming an adhesion species on at least one sidewall of the memory stack using a plasma doping process; and forming a sidewall liner on the at least one sidewall of the memory stack such that the adhesion species intermixes with an element of the memory stack and the sidewall liner.
 2. The method of claim 1, wherein forming the adhesion species comprises implanting the adhesion species into each sidewall of the memory stack.
 3. The method of claim 2, wherein implanting the adhesion species comprises performing a plasma immersion process.
 4. The method of claim 3, wherein performing the plasma immersion process comprises performing the plasma doping of boron on electrodes of the memory stack.
 5. The method of claim 1, wherein forming the adhesion species comprises subjecting the at least one sidewall to boron triflouride (BF₃).
 6. The method of claim 1, wherein forming the memory stack out of a plurality of elements comprises: forming a word line material; forming a first electrode material over the word line material; forming a selector device material over the first electrode material; forming a second electrode material over the selector device material; forming a phase change material over the second electrode material; and forming a third electrode material over the phase change material.
 7. The method of claim 6, wherein the first, second, and third electrode materials include carbon.
 8. The method of claim 6, wherein a boron adhesion species terminates unsatisfied atomic bonds of the carbon and a liner material.
 9. The method of claim 6, wherein forming the word line material comprises forming a material including tungsten.
 10. A method for fabricating a memory device comprising: forming a plurality of memory stacks, each memory stack formed by: forming a first carbon electrode over a word line material; forming a selector device material over the first carbon electrode; forming a second carbon electrode over the selector device material; forming a phase change material over the second carbon electrode; forming a third carbon electrode over the phase change material; patterning and etching the selector device material, the first, second, and third carbon electrodes, and the phase change material to form the plurality of memory stacks; and implanting a boron adhesion species into the sidewalls of the memory stack using a plasma doping process; and forming a liner material on the sidewalls of each memory stack wherein the boron adhesion species intermixes with an element of the memory stack and the sidewall liner to terminate unsatisfied atomic bonds of the element and the sidewall liner.
 11. The method of claim 10, wherein implanting the boron adhesion species into the sidewalls using a plasma doping process comprises performing a conformal doping process.
 12. The method of claim 10, wherein forming the liner material comprises forming a dielectric material.
 13. The method of claim 12, further comprising intermixing the adhesion species with the carbon in the first, second, and/or third carbon electrodes and the dielectric material of the liner material. 